BLOGS

We all have our favorite capacity/organ that we fail modern-day AI for not having, and that we think it needs to have to get truly intelligent machines. For some it’s consciousness, for others it is common sense, emotion, heart, or soul. What if it came down to a gut? That we need to make our AI have the capacity to get hungry, and slake that hunger with food, for the next real breakthrough? There’s some new information on the role of gut microbes in brain development that’s worth some mental mastication in this regard (PNAS via PhysOrg).

Rochellys Diaz Heijtza and Sven Pettersson and colleagues raised mice in a germ free environment and compared them to mice raised with normal gut bugs. The researchers found that compared to the germ-free mice, the normal mice had reduced expression of two brain molecules, synaptophysin, and PSD-95, in a region of the brain called the striatum. Correlating with this, the germ-free mice had higher levels of activity, and less anxiety than the mice with the normal complement of gut microbes. Amazingly, they also found that there was a “sensitive period” of exposure — a time before which exposure to the gut bugs mattered, and after which exposure didn’t change the brain any more. This is characteristic of many brain regions such as visual cortex, which needs normal visual input to develop properly and provide normal visual ability. If you provide that normal input after the sensitive period, the brain doesn’t fix itself. The scientists found that exposing the germ-free mice to normal gut microbes up to about 6 weeks of age resulted in normal levels of movement and anxiety; but exposure after that age resulted in no change.

How can this be? The paper has some specific technical suggestions, but if you think broadly about animals versus plants, it isn’t completely surprising. Next time you are eating your salad, consider how it is that you ended up eating your greens, rather than the greens eating you. It’s a story that’s almost two billion years in the making.

About 1.6 billion years ago, animals and plants went on their separate ways. One type of organism has the “stay in place and absorb” energy strategy. These are the plants, which sit and photosynthesize all day. The other organism has the “go around and get it” energy strategy – that’s you. The innovation of being an animal, in comparison to plants, is to have a gut with an ability to move, and a nervous system to detect the next good thing to put into that gut and then control the movement system to get the gut to the food.

The correspondence between a mobile gut and having a nervous system is so deep that some animals that give up mobility later in life also lose their nervous system. Ironically, they digest it. This is the tunicate, an animal that swims around in early life, but once they mature, they find a place to settle down on the ocean floor. Having done that, they digest most of their nervous system (some have compared this to getting tenure).

So, it is not a big surprise that key neurotransmitters like serotonin (most of which is excreted by cells in the gut wall in response to food), dopamine, glutamate, GABA, and norepinephrine are heavily represented in the gut, or that the gut is equipped with its own nervous system that has some one hundred million neurons, and almost the same number of types of neurons as the brain (Heribert Watzke has a stimulating TED talk on this).

I know what you’re thinking. This is just a story of how brains came to be. For the purposes of intelligence, the energy may as well come from a portable fusion reactor for all it matters. So any suggestion that AI needs a gut to reach the next level is misguided. I’ll argue that this viewpoint is overly simplistic.

Years ago the philosopher Patricia Churchland and the computational neuroscientist Terrence Sejnowski wrote a book called “The Computational Brain.” In it, they made a striking point regarding a pervasive belief in the AI community regarding the study of the brain. Most of the AI community view the key cognitive powers they are chasing as logically independent of any specific implementation. That is, it’s a formal system they are trying to uncover, and whether that formal system is encoded in silicon, punch cards, a hydraulic machine, biological material, or whatever, does not matter, just as whether the pieces of a chess game are made out of plastic or wood, or pictures on a computer screen, doesn’t matter. Because of this—the multiple realizability of formal systems–some people in AI believe that study the brain is irrelevant.

The brilliant point that Churchland and Sejnowski made was that, although it is true that once you understand the mechanism of the brain, at least certain parts of it may be formally independent of any particular instantiation, the key question for humanity right now is how do we get to this understanding. To get there, they said, we might take our cue from the only existing examples of things that are truly intelligent: animals. We need to study how real examples of intelligence work, crack their mechanism in their full wetware glory, and after that, we can potentially formalize and instantiate in silicon or whatever material we want.

Until recently, most of neuroscience had little inclination to mine questions of how appetitive drives such as hunger, and motivations in general, feed into the rich biomechanical and neuronal story that is being uncovered through the mechanistic study of animals. And yet, as I wrote above, the acquisition of energy through moving the gut around is foundational to “animal-hood” in the first place. Studies like the one showing ties between brain development and the gut testify to the deep interconnections of nervous systems and the guts they evolved to satisfy.

We have every reason to think that a full understanding of gut-brain interactions, and associated reward systems, will lead to a better understanding of how to build an intelligent machine. From this understanding we are also more likely to be able to build machines with the “right” connection between motivations and action, a central issue for people concerned about the consequences of The Singularity for the future of our species.

Comments (4)

I agree about the depth of the connection between the control of movement or action, braininess, and gutness. Adopting a view whereby perception and action are tied together has, I think, paid dividends for the understanding of vision, and the incorporation of the gut into the picture here is especially interesting. The same is likely true for intelligence more generally, especially in the realm of the dreams of AI. But since there are special reasons to think that perception and action are tied together because action is what perception is for, I’d be curious to know why you might expect this to carry over to so-called “off-line” aspects of intelligence, and whether there is anything out there on the gut in non-visual contexts.

So a brain is really the gut’s way to get fed. And a gut is the brain’s way to acquire its own kind of food via the blood supply. Who’s zoomin’ who?

They are zoomin’ each other. The original study is showing that how risky a mouse is in its environment is modulated by gut microbes. The general nature of the effect of environmental conditions on the development of nervous systems seems to be modulatory, establishing setpoints in behavioral reactivity that are well-tuned to the specific environmental conditions the animal is developing within. It’s tempting to speculate that the reason germ-free mice are more prone to risky behavior is that a reduced gut microbe load might arise due to scarcity of food supplies, so behaving in a more risky manner is necessary for survival.

For any given behaving agent with appetites, a proper way to set priority of pursuit of those appetites against the potential risk to survival is needed. If you buy the suggestion that the gut microbes are participating in establishing these priorities, we have this link at least. This would then input into planning systems that assess different potential futures to a goal, and pick one with the right mix of risk and payoff. At least prior to action, this would qualify as influencing an off-line aspect of intelligence.

I would argue that the role of the gut in biological intelligence is as a source of a positive drive. Specifically, the need to eat, or acquire energy.

AI researchers attempting to produce machines with behaviour often find that they need a system of competing and interacting positive and negative drives. “Seek such-and-such, it’s good”. “Avoid so-and-so, it’s bad”.

If you do not do so, you wind up with an AI that quickly goes to one place or state and then simply stays there indefinitely. The machine immediately optimizes it’s state and, because it’s rule set is too simple, there’s nothing else to do.

Brian – well put. The paper suggests there may be more too it though too. Messing with the development of the brain, in an area which sets how risky a behavior an animal picks, suggests it is not just the source of drive, but also part of the enormously complex task of adjusting phenotypic expression to match the unique environmental circumstances of each organism.